ATLANTA — Nearly 17 percent of U.S. medical costs can be blamed on obesity, according to new research that suggests the nation's weight problem may be having close to twice the impact on medical spending as previously estimated.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

One expert acknowledged that past estimates likely low-balled the costs and said the new study — which places obesity-related medical costs at around $168 billion — probably is closer to the truth.

"I think these are the most recent and perhaps statistically sound estimates that have come out to date," said Kenneth Thorpe, a health policy researcher at Emory University who has focused on the cost of health care.

The new research was done by John Cawley of Cornell University and Chad Meyerhoefer of Lehigh University. It was released this week by the National Bureau of Economic Research, a nonprofit, nonpartisan research organization.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

An influential recent study released last year — which has been cited by federal health officials — estimated that obesity-related medical costs have reached $147 billion, or about 9 percent of total medical costs.

The earlier study also estimated that obesity adds about $1,400 to a person's annual medical bills. The new study suggests the added cost is double that, exceeding $2,800.

Cawley and Meyerhoefer used a data base that other obesity researchers have used — a federal survey of U.S. citizens and their doctors and other medical providers, which is considered the most complete information on the cost and use of health care in the country.

The new study looked at the data base's information on nearly 24,000 non-elderly adult patients from the years 2000 through 2005. Results were reported in 2005 dollars.

Why did Cawley and Meyerhoefer come up with larger estimates?

Past studies have relied just on self-reported weight, and many people understate their actual weight. The new research made statistical adjustments to come up with what are believed to be truer figures.

The authors tried to better establish that excess weight was a cause for the medical costs. Previous studies stopped short of saying obesity caused the costs because there was too great a chance other factors could be responsible. Cawley and Meyerhoefer tried to overcome that problem by also looking at the weight of study subjects' relatives to determine if obesity ran in the family. If so, they labeled the medical costs of a fat person in that family to be caused by obesity.

The two researchers at first were a bit surprised by how large their estimates were, but obesity is clearly a major burden on society, said Cawley, an associate professor of policy analysis and management.

"It's hard to find conditions that aren't worsened or made more expensive by obesity," he said.

Thorpe said the new estimates highlight a need to invest more in obesity-fighting programs.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.